This invention relates to image recording methods, and more particularly it is concerned with a method of image recording information on a nonmagnetic sheet such as paper by using a magnetic recording member.
Heretofore, an image recording method is known in which a laser, particularly a semiconductor laser of compact size, is used to scan a photosensitive member that is charged beforehand, to form an electrostatic latent image thereon which is then developed into visible images to produce a duplicate of the document. As is well known, the electrophotographic process contains the steps of charging, exposing, developing and transfer-printing, and the surface of the photosensitive member is uniformly charged at a predetermined polarity. Upon the charged photosensitive member being exposed to an optical image of the documents to be copied, the charged photosensitive member is selectively discharged depending on the brightness of the optical image, to form an electrostatic latent image corresponding to the document. Meanwhile in a recording method using a laser, exposing of the charged photosensitive member by an optical image of the original is replaced by scanning for writing information to the photosensitive member carried out with a laser beam which is modulated by image signals produced by a solid state image sensor as a result of scanning. Such recording method raises the problem that difficulties are encountered in carrying out recording at high speed due to limitations placed by the spectral sensitivity of the photosensitive member because the light beam emitted by the laser has a wavelength in the range between 600 and 900 nm in the vicinity of visible rays. The image signals produced as a result of scanning to read out information by means of the solid state image sensor have their power varied depending on the image regions (dark regions) of the document. Thus the electrostatic latent image produced by scanning carried out with the laser beam to write information to the photosensitive member is a negative latent image having a low potential in portions of the photosensitive member corresponding to the image regions (dark regions) of the document, and it is necessary to carry out developing in the form of an inverse developing to develop such negative latent image into a positive image. This makes it impossible to use a developing agent that is commonly used in the ordinary electrophotographic printing process.
In another image recording method known in the art using a laser, the laser functions as a heat source. In this method, a heat sensitive sheet is used which has a coating of a chemical that develops color upon being heated. This recording method makes it impossible to use ordinary plain paper as copy sheets, thereby increasing running cost and rendering the recording sheets conspicuous by their unusualness.
In still another image recording method known in the art, a magnetic latent image is formed either by magnetizing a magnetic recording member by magnetic signals corresponding to information that is to be recorded (printed) or by scanning a uniformly magnetized magnetic recording member with a laser beam modulated by the signals to form a magnetic latent image. Such magnetic latent image is then developed by using a magnetic toner to produce a toner image which is printed by transfer-printing on a nonmagnetic sheet and fixed to produce a recorded (printed) sheet.
In the conventional image recording methods referred to hereinabove, the magnetic recording member is repeatedly used by directly developing the magnetic latent image formed on the magnetic recording member. The methods suffer the following disadvantages:
(1) It is necessary to carry out cleaning of the magnetic recording member each time printing is carried out, to remove the residual magnetic toner therefrom, and cleaning renders the recording apparatus complex in construction. PA1 (2) Even if cleaning is carried out each time printing is performed, it would be difficult to remove all the residual toner from the magnetic recording member, and the residual toner might contaminate the nonmagnetic sheet in the following transfer-printing operation. PA1 (3) A developing station, a cleaning station and in some cases a magnetic recording head might be brought into direct contact with the magnetic recording member, and this might shorten the service life of the magnetic recording member due to wear caused on its surface and deterioration thereof. PA1 (4) It is necessary to erase the residual magnetic latent image on the magnetic recording member following transfer-printing of the visible image, each time printing is carried out. This makes it necessary to use a demagnetizing device which renders the printing apparatus complex in construction. Particularly when a demagnetizing head is used as an erasing device, the demagnetizing head and the magnetic recording member suffer wear and deterioration because they are directly brought into contact with each other, thereby shortening the service lives thereof and making it difficult to perform high speed printing.